Signaling system



a y 1 I W @ck P. HUSTA SIGNALING SYSTEM Filed Sept. 7, 1921 IHIV Patented Get. 28, 1924.

UNITED STATES PATENT OFFICE.

PHILIP HUSTA, OF CORONA, NEW YORK, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, l\T.- Y., A CORPORATION O'F'NEW YORK.

SIGNALING SYSTEIuT.

Application filled September '7, 1921. Serial No. 499,101.

I '0 all whom it may concern.

Be it known that I, PHILIP HUs'rA, a citizen of the United States, residing at Corona, in the county of Queens, State of New York, have invented certain new and useful Improvements in Signaling Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to signaling sys tems and more particularly to methods and means for transmitting to a calling subscribers station an audible ringing signal to indicate that the called subscribers station is being signaled.

In some circuits of this nature the character of the signaling tone which the calling subscriber hears while waiting for the called subscriber to answer is subject to considerable variation, due to a number of causes. Heretofore it has been the usual practice to obtain the signaling: tone by completing the ringing circuit of the called subscribers station through one Winding of the repeating coil of the connecting link circuit, the tone that the calling subscriber hears being obtained by induction through the windings of the repeating coil. This tone is due to the audible higher harmonics of the ringing current and it is found that these generally differ with each source of ringing current supplied. Another. varia ,tion is caused by the variable volume of the ringing current due to lack of uniformity in the resistance of the called subscribers line; in the case of long lines the tone is weak and the opposite is true for short lines. Again, the tone varies with the number of subscribers in the same central oflice being simultaneously signaled and with the voltage of the source of ringing current.

It is an object of this invention to provide methods and means for employment preferably in present equipments to furnish an audible ringing signal wherein the disad vantages described above are avoided, and

further to attain this without destroying the electrical continuity of the calling and the called ends of the link circuit, soas to avoid any extensive or disturbing change in such equipments.

To attain this object in accordance with one feature of the invention a separate source of signaling current is provided. This current is generated in a circuit of comparatively high impedance. In this circuit is also located a low impedance section, and through this section there is also passed the regular ringing current as well as the audible ringing signal current. Because of the constancy of the potential drop of this audible ringing signal current across the low impedance section a substantially constant tone is supplied to the calling subscriber irrespective of variations in the character of the regular ringing current used to signal the station of the called subscriber and which may be due to the causes outlined above.

For a more complete understanding of the invention reference may be had to the following description in connection with the accompanying drawing Fig. l of which illustrates one embodiment of the invention and Figs. 2, 3 and 4 of which show, respec tively. the wave forms of the output of the ringing generator, of, the signaling current transmitted to the calling subscriber in one of the above mentioned systems widely in use and of the signaling current transmitted to the calling subscriber in accordance with the embodiment of the invention shown in Fig. 1.

The drawing shows two subscribers sta tions A and B connected. by a link circuit L, which link circuit is arranged in the manner well known, to automatically supply to the called station B ringing current from a source 1. \Vhile the station B is being signaled, a portion ofringing current'passes to ground through the upper right-hand winding of a repeating coil 2, and another portion to ground through a low impedance path through the resistance 3 by way of the upper alternate contact of ringing relay at which is actuated when the plug 5 is inserted into the jack 6. Owing to the low impedance of the path through resistance 3 only a small volume of the audible components of the ringing current from source 1 is passed through the comparatively higher impedance path of the repeating coil winding.

owever, a high speed interrupter 7 in series with grounded battery supplies to the path 3 through the contacts of a relay 8 and the windings of a transformer 9 and its associated apparatus a volume of audible ringing signal current many times greater than that obtained from the audible components of source 1. This preponderance of ringing signal current from the interrupter circuit renders the signaling tone furnished to the calling subscribers station A substantially constant. independent of the variations of current from the source 1. 7

As shown in Fig. 2 the current produced by the source 1 possesses numerous harmonics which affectthe wave form of. such current. As previously mentioned, in one system widely in use the higher of such harmonics superimposed upon the 16-cycle current are transmitted to the calling subscriber througlra repeating coil similar to repeating coil 2. In such a case the current wave flowing over the calling line assumes, in general, the resultant of the waveforms shown in Fig. Although there may be many more harmonics present, only a suflicient number have been shown toillustrate the form produced; This current has been found to produce a distinctive and pleasing tone in the calling subscribers receiver. The current produced by'means of the battery, the commutator, the repeating coil 9 and other associated apparatus is of a single unmodulated frequency as shown in Fig. 4. The frequency of this latter current has been selected to correspond. with one of thosewhich predominate in the wave shown in Fig. 3and therefore such current produces a distinctive constant tone in the calling subscribers receiver which is entirely independent of any variations in current produced by the ringing current source .1.

It is thought that the invention may be more fully comprehended from the follow ing detailed description of the'operation of the circuit.

Assuming that the subscriber of station A desires a conversational connection with the subscriber of station B whose line is one of a plurality ofsimilarlines terminat ingat a switchboard in thesame officewith the line of subscriber A or in a distantoffi'ce, and that a connection with the calling subscriber A has been established inthe usual way, the operator in the well'known mannercompletesthe connection desired by inserting plug 5 of'the link circuit L into jack 6. An operative circuit for relay 4 is then completed which may be traced from grounded battery, through the winding of relay 4:, contact of marginal tripping relay 10, right-hand contact of relay 11, (said contacts short circuiting'the winding of'relay 11'), sleeve contacts of'plug 6, and resistance 12 to ground. Ringing current from source '1 is now supplied vto the subscribersstation B over the following path: source of ringing current 1, collector ringl conducting'segment 24 of interrupter 14;, winding of relay 10, which does not operate until the subscriber ofstation B responds, lower alternate contact of relay 1, ring contacts of plug '5' and jack 6, apparatus of station E, tip contacts of jack 6 5 and jack and. plug 5, and then to ground through parallel paths comprising the upper righthand winding of repeatin coil 2 and the resistance 3, the latter pati by way of the upper alternate contact of relay 4.

The subscriber of station A listening for the subscriber at station E to answer, hears but a small volume of tone due to the audible components of the ringing source 1, by reason of the marked shunting effect of the low impedance path through resistance 3. However, when the brush of interrupter 14 is in contact with the segment 24:, relay 8 is energized over an obvious circuit which includes the condenser 15. This causes interrupted battery current to be supplied over a circuit from grounded battery,'interrupter 7 contact of relayS, and to ground through the primary windings 16 of 'the transformer 9. In shunt" with these windings16 area resistance 17 and a condenser 18 so designed as to prevent sparking at the brushes of the interrupter 7 and to improve the wave form of the output; The interrupter and associated circuits are designed to supply signaling current of any convenient audible frequency. The efiect of this arrangement is to supply through the secondary winding'19, coil 20and condenser 21, a current of audible frequency.

From the upper terminal of resistance 3 a circuit may be traced through the; upper alternate contact of relay 4 and the upper right-hand winding of repeating coil 2 to ground. Accordingly the 'potentiahdrop across resistance 3 is effective in producing by induction through the windings of repeating coil 2, the transmission; of a signaling tone tostation A. The volume of this tone can conveniently be made many tiines greaterthanthe volumeof tone due to the higher: harmonic components from. the source of ringing-current 1. Therefore, the character oftli'is tone depends principally upon the frequency-of the interrupter 7 and is practically independent ofthe'tone due to source 1, as appears fromthe: following.

If the resistance of the line ofa called station B varies, it is obvious that the'volume of current from source 1 passing through the upper right-hand winding: of the repeatingcoil2 also varies accordingly. Similarly therelis a current variationdepending upon the voltage of the current of source 1 and upon. the number of called stations being-signaled simultaneously over the conductors 22, 23, leading-to other link circuits similar to link circuit L. 'There is also a variation in: signaling tone from source 1 depending upon the magnitude of its audible harmonic components. However, all these possible sources ofv'ariation are without effect by reason of the preponderating effect of the tone from interrupter 7 The low impedance path through resistance 3 has the desirable characteristic of effectively shunting away from the winding of the repeating coil 2 ringing current from source 1, and by reason of its low impedence compared to the impedance of the apparatus with which it is in series and of the multiple paths through the upper right-hand windings of the repeating coils of other link circuits, an unappreciablc change in the potential drop across it results by reason of a variation in the -numher of called stations being signaled.

Inasmuch as the link circuit L shown on the drawing is well known in the art and is not part of this invention, only so much thereof as is necessary to an understanding of the invention has been disclosed and described herein. The circuit arrangements employed at stations A and B have been omitted since they may be of any usual type.

What is claimed is: .;i

1. In a telephone exchange system, a calling subscribers station, a called subscribers station, a link circuit for interconnecting said Calling and called stations, a source of signaling current of variable voltage for signaling the called subscribersstation, a second source of signaling tone current for signaling the calling subscribers station that the called subscribers station is being called, and a relay operated by current from said first mentioned source for transmitting from said second source of signaling current to said calling subscribers station a Volume of signaling tone substantiallyinclependent of variations in the voltage of said first mentioned source of signaling current.

2. I11 a telephone exchange system, a calling subscribers station, a called subscribers station, a link circuit for interconnecting said stations, a source of signaling current for calling the called subscribers station, said source of current having harmonic components of audible frequency, a source of s'ignaling tone current for signaling the calling subscribers station that the station of the called subscriber is being called, and means for transmitting from said source of signaling tone current to said calling subscribers station, a volume of signaling tone substantially independent of variations in the harmonic components of the said first mentioned source of signaling currents, the electrical continuity of the link circuit between the calling and called subscribers stations being maintained while the called subscribers station is being called.

3. In a telephone exchange system, a plurality of calling subscribers stations, a plurality of called subscribers stations, 2. plurality of link circuits for interconnecting calling and called stations, a source of signaling current of Variable voltage for calling called subscribers stations, a source of naled simultaneously, the electrical continuity of the link circuits between'the said calling and called subscribers stations being maintained 'while the called subscribers stations are being called.

4. In a telephone exchange system, a calling subscribers station, a called subscribers station, a link circuit for interconnecting said stations, a source ofrlnging current for signaling the called subscribers station, a

source of signaling tone current to signal the calling subscrlbers station that the called subscribers station is being called, a high impedance local'circuit for said source of signaling tone current including a low impedance section, means for completing a ringing circuit for the called subscribers station through said low impedance section, means for using the potential drop across said low impedance section to supply to the calling subscribers station audible ringing tone of a Volume substantially constant and independent of the efliect of variations in said source of ringing current, the electrical continuity of the link circuit between the calling and called subscribers station being maintained while the called subscribers station is being called.

5. In a telephone exchange system, a calling subscribers station, a called subscribers station, a link circuit for interconnecting said stations, a source of signaling current of variable voltage for signaling said called subscribers station, a source of audible signaling tone resident in said source of sig naling current as audible higher harmonics thereof, a source of signaling tone current for signaling the calling subscribers station that the station of the called subscriber is being called, and means for transmitting from said source of signaling tone current to said calling subscribers station a volume of signaling tone substantially independent of the variations in the volume of the higher harmonic components resident in the first mentioned source of signaling current, the continuity of the link circuit between the stations being maintained while the called subscribers station is being called.

6. A telephone system comprising a calling and a called station, a source of ringing current connected thereto, and means comprising a relay responsive to current from said source for sending a tone to said calling station.

7, A telephone system comprising a calling;station,.a called: station, a sourcerofringing currentelectrically connected to both of saidstations, a" shunt path between said source and said calling station for. reducing the intensity of the ringing current supplied to said calling station, and a; separate-source of ringing current. for said calling station.

source of ringing; current,and a relay I re- SPOllSlVQ tov cur-rent supplied by one of said sources for. connecting said other source to thecalllng station.

10; The method of. signaling to. calling stations which comprises supplying. to: each of said stations signaling. current of substantially the same intensity and independent. of the-length of the called subscribers loop.

11. A telephone system comprising. a plurality of stations, a plurality ofsourcesof signaling, current,-,a plurality of paths for supplying signaling current from said sources to said-stations, and ineans responsive. to current. in one of said paths for controlling .another of said paths.

12. A telephone system comprisinga calling'line, a called-line, a distinct source of signaling current for each "of said lines, a

plurality of paths forsupplying signaling current'from said sources'to. said lines, and a relay included 111 and: responsive to current in one of said paths to control the current in another'of said paths.

In Witness whereof, I hereunto subscribe my name this 31st day of August A;. D:, 1921.

PHILIP HUsTA 

